Geometric shape of the support surface of the piston

Geometry of the slot between piston bearing surface and cylinder bore affects the friction losses of the IC engine to the far extent. It appears that these losses depend more on the area covered with oil than the thickness of oil layer separating collaborating parts. Barrel-shaped or stepwise piston bearing surface is the way to reduce the oil-covered area. The first concept has been used for years while the stepwise profile has not been applied for various reasons, although this idea providing higher load capacity of oil layer in stepwise slot was published in literature in the fifties of twentieth century. The stepwise profile can be obtained covering the cylindrical or tapered piston-bearing surface with a thin layer graphite. This paper presents the results of simulation leading to the reduction in friction losses and abrasive wear of piston bearing surface and cylinder bore. Covering the piston bearing surface with a thin layer of graphite one can get an extremely advantageous tribological properties of the piston assembly which means the expected parameters of oil film and in a case of film rupture – an ignorable abrasive wear of the graphite layer and/or cylinder bore.